246
FXUS62 KGSP 150653
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
253 AM EDT Thu Aug 15 2024

.SYNOPSIS...
Dry high pressure gradually builds in from the north today,
resulting in isolated afternoon showers in the mountains. The high
will drift off the East Coast Friday as a cold front approaches
from the west this weekend, bringing better coverage of showers
and thunderstorms. Drier conditions will return behind the front
as well as near normal temperatures early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Messages:

1) Another Round of Patchy to Locally Dense Fog Expected Across
Portions of Western North Carolina This Morning

2) Below Normal High Temperatures Return Today for Most Locations

3) Isolated Showers Will Develop Across the Mountains Again this
Afternoon and Early Evening

As of 230 AM EDT Thursday: Today`s forecast is nearly a repeat of
yesterday. Patchy to locally dense fog should develop again this
morning across portions of western North Carolina. KAVL has already
seen dense fog and low stratus develop, with the ASOS having already
reported 1/2 to 3/4 mile visibility. We will monitor the need for
another possible fog SPS throughout the next few hours. Any fog and
low stratus that develops should mix out shortly after sunrise.
Seeing isolated showers lingering across extreme northeast Georgia
this morning and the 00Z CAMs show this activity lingering, or even
expanding in coverage, through the morning hours. Thus, maintained
chance PoPs across these zones through this morning. Broken to
overcast cloud cover is in place across the western SC Upstate,
extreme northeast GA, and the southwest NC mountains and should
linger through the morning hours. This cloud cover may even limit
fog formation over the Little TN Valley through daybreak. Lows this
morning should drop near to just below climo along/near I-77 with
lows remaining a few degrees above climo elsewhere.

Highs today will be similar to yesterday`s, remaining near climo to
a few degrees below climo. Temperatures will be slightly cooler in
the mountains but slightly warmer east of the mountains this
afternoon. 00Z CAMs show the potential for isolated showers develop
once again across the mountains this afternoon and early evening.
Instability looks even lower than yesterday, not exceeding 500 J/kg,
so did not go with any mentionable thunder chances. May see a bit
more cloud cover today thanks to sfc winds gradually turning S`ly.
Lows tonight should end up a few degrees above climo area-wide
thanks to some lingering cloud cover. Another round of low stratus
and fog may develop again tonight but guidance keeps it confined to
the mountain valleys for now.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 230 AM EDT Thursday: An upper trough will dig into the Ohio
Valley Friday thru Saturday, bringing an associated cold front
toward the Southern Appalachians.  An increasing SWLY 850mb
flow ahead of the front will bring moisture to the mountains
and should aid in solid chance PoPs with daytime heating Friday
aftn and evening.  30-40 kt of bulk shear may support some
organized convection upstream, with a marginal risk of severe
storms across the NC mountains. The main threat will likely be
damaging wind gusts. The environment east of the mountains will
remain less unstable, but westerly steering flow may bring some
of the convective activity into the Piedmont (as the 00z HRRR
suggests). Even if that happens, convection should generally weaken
as it tracks east. PWATs increase to 1.75-2.0", so there will be
a threat for locally heavy rainfall.  Highs will be slightly above
normal, especially east of the mountains where there will be less
cloud cover. Lows will be near to slightly above normal.

The front should be pushing into the forecast area (or at least
be close just to the west) on Saturday. The front combined with
mid-level troughing and increasing NWLY flow should result in a
relatively active day convectively. With that said, instability
looks modest, and shear will be marginal.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 240 AM EDT Thursday: The medium range guidance still agrees on
a deep longwave trough setting up roughly along the East Coast. The
00z GFS is in line with the 12z ECMWF and Canadian on a slightly
slower progression, resulting in the cold front lingering across
the eastern part of the CWA on Sunday. The front still over the
Piedmont on Sunday may result in another round of convection,
but any severe threat would probably be confined to the southeast
edge of the forecast area.

On Monday the upper trough axis will be overhead and moist NWLY
flow will support showers and a few storms across the mountains,
but it will be generally dry east.  Dry air finally works in Tuesday
under deep-layer NWLY flow. Models disagree on what happens to the
upper trough Wednesday, with the ECMWF closing off an upper low over
the Northeast, while the GFS digs a much more aggressive trough
into the Great Lakes. The Canadian is in between with a trough
axis still over the forecast area. Despite those differences,
they all generally agree on relatively dry weather continuing on
Wednesday. Temps will be near to slightly below normal.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
Key Messages:

1) Patchy to Dense Fog and Low Stratus Possible again this morning
at KHKY and KAVL

2) Isolated Showers will Develop Again Across the Mountains this
Afternoon

3) Mostly MVFR to VFR through the 06Z TAF Period

At KCLT and elsewhere: The 06Z TAF period will be similar to what we
saw yesterday. Another round of mountain valley fog and low stratus
is expected through daybreak, with activity potentially reaching
KHKY. KAVL has already seen LIFR fog and cigs develop this morning
so have a TEMPO through the early morning hours. KHKY has not yet
seen restrictions from stratus or fog so the thinking is that
terminal will have a lower chance of dense fog this morning.
Nonetheless, went with a TEMPO with IFR fog and LIFR cigs at KHKY
but backed off on the potential for dense fog. Patchy fog may
develop east of the mountains but is generally not expected to have
a major impact on the remaining TAF sites. It will remain dry east
of the mountains again today, with KAVL having the best potential to
see some showers around the terminal. Held off on a mention for VCSH
or -SHRA for now as confidence is too low on whether activity will
develop directly over or near the terminal. Winds will be calm to
light NE east of the mountains, with calm to light SE winds at KAVL
through daybreak. Winds will remain S/SE at KAVL through the period,
with winds east of the mountains gradually turning S/SE this morning.

Outlook: Coverage of convection increases Friday as a cold front
approaches out of the west. The cold front will track over the
forecast area this weekend keeping convection around. Drier
conditions return behind the front early next week. Patchy fog and
low stratus will be possible each morning in the mountain valleys
and in any locations that received heavy rainfall the day prior.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$

SYNOPSIS...ARK
NEAR TERM...AR
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...AR